For diagnostic examination purposes and for interventional procedures, for example in cardiology, radiology and neurosurgery, interventional X-ray systems are used for imaging whose typical major features can be, for example, a robot-controlled C-arm on which an X-ray tube and a X-ray detector are mounted, a patient examination table, a high-voltage generator for generating the tube voltage, a system control unit, and an imaging system including at least one monitor. A C-arm X-ray machine of said type, as illustrated in FIG. 1 for example, has a C-arm 2 which is rotatably mounted on a stand in the form of a six-axis industrial or articulated robot 1 and at the ends of which X-ray radiation source, for example an X-ray emitter 3 with X-ray tube and collimator, and an X-ray image detector 4 are mounted as the image recording unit.
By means of the articulated robot 1, known from U.S. Pat. No. 7,500,784 B2 for example, which preferably has six axes of rotation and consequently six degrees of freedom, the C-arm 2 can be moved arbitrarily in three dimensions, for example by its being rotated about a center of rotation between the X-ray emitter 3 and the X-ray detector 4. The inventive X-ray system 1 to 4 can be rotated in particular about centers of rotation and axes of rotation in the C-arm plane of the X-ray image detector 4, preferably about the axes of rotation intersecting the center point of the X-ray image detector 4 and the center point of the X-ray image detector 4.
The known articulated robot 1 has a base frame which is permanently installed on a floor, for example. Secured thereto is a turntable which is rotatable about a first axis of rotation. Attached to the turntable so as to be capable of pivoting about a second axis of rotation is a robotic floating link to which a robotic arm is fixed so as to be rotatable about a third axis of rotation. A robotic hand is attached to the end of the robotic arm so as to be rotatable about a fourth axis of rotation. The robotic hand has a securing element for the C-arm 2 which can be pivoted about a fifth axis of rotation and rotated about a sixth axis of rotation running perpendicular thereto.
The implementation of the X-ray diagnostic apparatus is not dependent on the industrial robot. Conventional C-arm devices can also be used. It is also possible to use bi-plane systems which consist, for example, of two C-arm X-ray machines as shown in FIG. 1.
The X-ray image detector 4 can be a flat semiconductor detector, rectangular or square in shape, which is preferably produced from amorphous silicon (a-Si). However, integrating and possibly counting CMOS detectors can also be used.
A patient 6 to be examined is positioned in the beam path of the X-ray emitter 3 on a patient examination table 5 as the examination object for the purpose of recording the heart, for example. Connected to the X-ray diagnostic apparatus is a system control unit 7 having an image system 8 which receives and processes the image signals of the X-ray image detector 4 (operator control elements, for example, are not shown). The X-ray images can then be studied on a monitor 9.
Important methods in imaging with C-arm X-ray machines are                diagnostic imaging with                    cardangiography at medium X-ray doses, a native visualization of the coronary vessels with the aid of contrast agents,            digital subtraction angiography (DSA) for visualizing vessels exhibiting little movement with the aid of contrast agents, a method in which a native image is subtracted as what is termed a “mask” from a series of native images in which a vessel or vascular tree is filled with contrast agent, the anatomic background disappearing as a result of the subtraction and the vessel or vascular tree remaining visible on its own, and            3D imaging with or without contrast agent and                        interventional imaging with                    fluoroscopy or transillumination in which primarily the positioning of catheters, guide wires, balloon catheters, stents, etc. is effected using a small X-ray dose, this method also being used purely diagnostically in order to position a catheter for the application of contrast agent, and            roadmapping, in which, similarly to DSA, initially a mask, a native image of a vascular tree filled with contrast agent, is produced. Next a series of native images is generated in which a wire, for example, is moved. For subtraction of the mask image all anatomical structures disappear. All that remain visible are the vascular tree and the wire moved “therein”.                        
In addition to the methods mentioned here there are more advanced methods such as 3D roadmapping, for example.
In a known roadmap method, illustrated for example in FIG. 2, the following images are generated: a pure native image 10 (anatomy only) during the system dose regulation, a mask image 11, a native image from the fill phase in which the vascular tree 12 is filled with contrast agent, and a native image series 13 in which an object 14, a wire for example, is moved in the vascular tree 12 under fluoroscopy. From the fluoroscopy image series 13 in which the object 14 can be seen, the mask image 11 with vascular tree 12 filled with contrast agent is subtracted in a subtraction stage 15 and in an addition stage 16 a constant K for setting the mean grayscale value is added. Further image processing steps such as contrast adjustment, edge enhancement, etc. can follow until a current subtraction series 17 is obtained in which only the moving object 14 is still readily identifiable in the “frozen” vascular tree 12.